Bulk storage media, such as magnetic and optical storage media, often include defects, such as inconsistencies in a magnetic or optical coating or other surface anomalies, which make portions of the media unsuitable for data storage. However, it is often desirable to use media containing such defects, as these defective areas are generally relatively small compared to the total storage area of the media. Moreover, such defects may develop or be detected during normal use of the storage media. Therefore, schemes for identifying and avoiding these defective areas have been used.
Traditional schemes for defect management have been complex and inflexible. These schemes have relied on utilizing a portion of the media as a defect management area in order to present a media that, although including defective areas, appears as if it were defect free. Accordingly, upon a manufacturer's formatting of the media for subsequent use in data storage, an analysis of the storage areas is made and defective areas are marked as unusable. In order to provide media which includes a particular amount of available user storage area, logical addresses of the user data areas are “slipped” into the defect management area so as to omit the physical address of these defective areas and, thus, present defect free logical media.
However, as defects may develop or be discovered during actual use of the bulk storage media, there must also be a method of providing redirection for or replacement of defective areas discovered during use to available sparing areas. Accordingly, the systems operate to remap or redirect the logical address associated with an area determined defective to the logical address of a sparing area. Therefore, the manufacturer's initial formatting of the media includes establishing predefined user data areas and corresponding predefined sparing areas (defect redirection or remapping areas).
For example, with magneto-optical (MO) discs, the MO drive has to recognize the particular media and, thus, use predetermined data areas (user data areas) and predetermined sparing areas (defect redirection or remapping areas). Such sparing areas may be interspersed with the user data areas throughout the media at various intervals, thus establishing zones within the media wherein an amount of user data area and its corresponding sparing area are established. Therefore, defect management tables are provided to allow the drive to properly read and write user data within these zones without encountering a defective area. However, it should be appreciated that these prior art defect management tables store only a list of used sparing areas and, thus, require complex operations in order to determine sparing areas available for remapping.
On most media, regardless of the physical position of the tracks defined for data storage, the information density of these tracks remains constant. However, as tracks are established further out toward a circumferential edge of a media disc, the tracks themselves become larger. Therefore, there are more sectors per track available on tracks disposed radially toward the circumferential edge as compared to tracks disposed more radially inward. However, prior art systems tend to keep the zones a fixed radial width, i.e., each zone includes substantially the same number of tracks, which means that zones disposed further out toward the circumferential edge include more sectors than the ones further in because of the longer tracks included in the zones further out in diameter on the media surface.
For example, as the tracks become longer due to their concentric disposition on the media, a track eventually becomes large enough to allow an additional sector to be fit in (the generally adopted data formats of bulk storage media do not provide for partial sectors). Therefore, as the tracks become longer as they are established further out toward the circumferential edge, tracks are defined having increased space not quite sufficient to provide an additional sector. However, provided enough tracks are defined on the media, a track is established having sufficient length to provide a complete extra sector. This is a natural division point on the media for any kind of operation, such as the above described zone boundaries. Therefore, zones defined by this phenomena of the media, although having a constant information density, will provide differing amounts of data storage.
The prior art systems generally set aside more blocks for defect management (sparing blocks comprised of sparing sectors) within the zones disposed more toward the circumferential edge, such that a substantially constant ratio of defect management blocks to user data blocks are set aside for sparing. Thus, the intervals at which the sparing areas are spaced do not present a simple mathematical relationship and, accordingly, are not easily accessed without a defect management table including sufficient information to provide logical addressing for the irregular sparing intervals.
Furthermore, as the zones associated with the user data areas and the sparing areas are defined by the physical attributes of the media, the sparing portion of a zone may not always present a desired amount of sparing blocks nor a desired distribution upon the media. A prior art zone will include a particular number of total sectors due to its relationship to the physical attributes of the media. Accordingly, using an example of 1100 total sectors in a particular zone, if it is desired to provide 1000 sectors as free user data storage and 100 sectors of sparing, this may not be possible. If there are defective sectors within the 1000 sectors upon the manufacturer's formatting of the media, this deficiency in the user data storage space will be compensated for by slipping these defective sectors to the sparing sector. Thus, the sparing sectors will initially be short sectors from the desired total. Accordingly, there will not be the desired amount of sparing area available for sparing during actual use of the media.
Moreover, it should be appreciated that slipping of the defective storage areas into the sparing area is done in the prior art for each zone, i.e., user storage area and corresponding sparing area combination. Accordingly, the slipping mismatch resets itself at every zone. As slipping starts from the beginning of the zone, an actual implementation must determine for any operation, i.e., for a random sector read or write request, the system must determine how many sectors are listed in the defect list prior to that one but in that zone. Therefore the system must know the physical start address of the zone, and how many defects are listed between that address and the requested sector. Determining this information involves at least two lookups in the defect table.
Additionally, with prior art systems relying on physical phenomena in order to define zones, and therefore define sparing sector intervals, sparing is tied to the physical attributes of the media. However, a particular sparing scheme defined by the media's physical attributes may not be optimized for the particular environment in which the storage media is going to be used. For example, use of the media in environments which require streamed data, such as recording video or audio, may not benefit optimally from sparing intervals established as a function of the physical phenomena of the media.
Furthermore, the amount of space set aside for defect management cannot be changed in these prior art schemes, as the defect management techniques have written into the media standard itself the location for the sectors that are used for defect management. For example, a mass storage unit incorporating prior art defect management techniques will generally come from the manufacturer with certain areas set aside for defect management and the allocation of these areas could not be altered.
Therefore, a need exists in the art for a system and method for managing defects on bulk storage media which is simplified in its implementation.
A further need exists in the art for a defect management technique which is independent of physical characteristics of the bulk media.
A still further need in the art exists for the defect management technique to be configurable for the particular environment in which it is to be used.